Trailers used to haul loose materials such as dirt, sand, gravel, or grain commonly have beds or tubs that have an open top with generally vertical front and rear walls and sloping sidewalls for retaining contents within the trailer. Therefore, if the trailer bed is not covered as the trailer is pulled over the road, the loose contents may be blown and scattered out of the open top of the trailer bed. Additionally, the contents of the trailer bed may be compromised by rain, or other contaminants. Accordingly, it is known to deploy tarps across the open top space of the trailer beds to cover the contents of the trailer beds.
Several mechanisms have been devised for deploying the tarps across the trailer bed. Many of these devices include radial arms that are rotatably mounted at the front and rear of the tub and have a roll of tarp disposed between them. As the radial arms rotate in one direction across the truck bed, the roll of tarp between the arms is unrolled to cover the contents of the truck bed. When the arms are rotated back in the opposite direction, the tarp is taken back up upon the roll to uncover the trailer bed. Examples of such devices may be seen in Searfoss, U.S. Pat. No. 6,206,449 and in Michel, U.S. Pat. No. 5,002,328.
For designs that use a pair of pivotally connected arms to form the radial arms, a problem can arise as the arms move across their length of greatest extent in that precaution must be taken to prevent the arms from pivoting over center, which will cause the system to bind. Heretofore that has been accomplished by a combination of springs that urge the arms toward the appropriate side of center alignment, and making the arms long enough that they do not approach alignment with each other at the areas of greatest extent. However, these solutions could be improved upon by eliminating the springs, which can be relatively expensive and time consuming to install, and by shortening the arms to reduce weight and save material. The present invention provides such a solution.